1. Field of the Invention
The present invention relates to an electrophotographic apparatus used for printing images on a recording paper sheet. In particular, the present invention relates to an electrophotographic apparatus incorporating a photosensitive drum.
2. Description of the Related Art
FIG. 34 of the accompanying drawings shows an example of conventional electrophotographic apparatus. The illustrated apparatus includes a photosensitive drum 1e and a plurality of peripheral devices arranged adjacent to the photosensitive drum. The peripheral devices may be a charging unit 8e, an exposing unit 3e, a developing unit 4e, a sheet transferring unit 5e, and a cleaning unit 6e. The charging unit 8e is used for charging the cylindrical outer surface of the drum 1e. The exposing unit 3e irradiates the charged outer surface of the drum with light so that a charged pattern corresponding to a selected image to be printed is formed on the outer surface of the drum 1e. The developing unit 4e supplies toner to the outer surface of the drum 1e for making visible (developing) the charged pattern of the selected image. The sheet transferring unit 5e serves to feed recording paper sheets 98 from a paper supply portion 99. Each of the recording paper sheets is brought into contact with the outer surface of the drum 1e, so that the toner-developed image (hereinafter, simply called "toner image") is transferred onto the recording paper sheet. The cleaning unit 6e serves to scrape remaining toner off the outer surface of the drum 1e. The recording paper sheet 98 carrying the toner image is sent to a fixing unit 97 for undergoing heat treatment so that the toner image is fixed to the paper sheet 98. Thereafter, the paper sheet 98 is forwarded to a recorded sheet stocker 96.
As is known, after the electrophotographic apparatus has been repeatedly used for a certain period of time, the outer surface of the drum may become difficult to be properly charged. In such an instance, the user may need to replace the photosensitive drum 1e with a new one.
For facilitating the replacement of the photosensitive drum 1e, conventionally, the drum is releasably mounted on a rotating shaft 2e. Specifically, referring to FIG. 35, the shaft 2e has a first end 2f and a second end 2g opposite to the first end. The first end 2f is rotatably supported by a cover member 7e via a bearing 80e fixed to the cover member. The cover member is releasably attached to a stationary chassis 9e. The first end 2f is screwed into a nut 95 for preventing the drum 1e from unduly coming off the shaft 2e. The second end 2g is supported by a fixing member 9f via a pair of bearings 81e.
With such an arrangement, the drum 1e is easily removed from the shaft 2e in the following manner. First, as shown in FIG. 36, the cover member 7e is detached from the chassis 9e. At this stage, the shaft 2e is supported only at the second end 2g by the two bearings 81e. Then, after the nut 95 is removed from the shaft 2e, the user can easily remove the drum 1e from the shaft 2e via the first end 2f. Thereafter, a new photosensitive drum is installed on the shaft 2e in the reversed manner.
In replacing the photosensitive drum 1e with a new one, the user should be careful enough not to cause those photosensitive drums (the old and new ones) to come into contact with the peripheral devices. If such contact occurs, the photosensitive drums (especially the outer surface of the new drum) and/or the peripheral devices may unfavorably be damaged, rendering the apparatus unable to perform proper image printing.
For avoiding the above problem, the peripheral devices of the conventional apparatus are arranged to be movable relative to the photosensitive drum. Specifically, the peripheral devices can be brought into two states, i.e., a set state where the peripheral units are positioned close to the outer surface of the drum 1e, and a release state where the peripheral units are sufficiently spaced away from the drum. With such an arrangement, by bringing the peripheral devices into the release states, it is possible for the user to perform the drum replacement without causing the drums and the peripheral devices to be damaged.
For more reliable protection of the drums and the peripheral devices, use may additionally be made of a guide rod 89e connected to the shaft 2e in longitudinal alignment therewith, as shown in FIG. 37. Such an arrangement is advantageous in that the drum 1e is moved only in its axial direction but not in its radial direction when removed from or installed onto the shaft 2e. As a result, unfavorable contact between the photosensitive drum and the peripheral devices can be avoided.
However, the conventional electrophotographic apparatus has been found still disadvantageous in the following points.
Specifically, with the nut 95 detached from the shaft 2e (see FIG. 36), nothing can stop the drum 1e from being removed from the shaft 2e. Thus, even though the guide rod 89e is ready for use, the user may not utilize it because he finds it troublesome or time-consuming to connect the rod to the shaft, or because he does not know how to use the guide rod.
Another disadvantage of the conventional apparatus is that the user may fail to remember fixing the positioning nut 95 to the shaft 2e after a new photosensitive drum is installed. In such an instance, the drum may unfavorably be displaced along the shaft 2e upon operation of the apparatus, which may cause damage to the drum and the peripheral devices.
Still further, in the conventional apparatus, the user may improperly try to remove the drum 1e from the shaft 2e before the peripheral devices are brought into the release states. In such an instance, since the peripheral devices are held close to or in contact with the outer surface of the drum 1e, the outer surface of the drum and/or the peripheral devices may be unfavorably damaged.